Unit 7 Flashcards
1
Q
How do exocrine glands develop?
A
Exocrine glands develop as invaginations of surface epithelium, induction by connective tissue
2
Q
How do exocrine glands retain surface connection?
A
Exocrine glands retain a connection with the surface via ducts.
3
Q
What is an acinus?
A
A berry-like cluster of cells with a central lumen that serves as the secretory portion of the secretory vesicles. It produces the secretory product.
4
Q
What is the conducting portion of a secretory vesicle?
A
A duct. It may be branched or unbranched. It modifies secretory product by absorption. Ducts may also have secretory functions in some glands.
5
Q
How are exocrine glands classified?
A
Simple glands: single unbranched duct. Secretory portion can be branched or unbranched. Examples: sweat glands and sebaceous glands.
Compound glands: multiple branched ducts. Secretory portion can be acing, tubular or tubloacinar. Examples: salivary glands and exocrine pancreas.
6
Q
What are the 3 different types of secretion?
A
Holocrine
Apocrine
Merocrine
7
Q
What is holocrine secretion?
A
Lysis of cells filled with secretory product. Cells divide and disintegrate, and their contents become the secretion. Example: skin sebaceous gland.
8
Q
What is apocrine secretion?
A
Shedding of apical cell segment filled with secretory product. The apical portion pinches off a secretory cell and enters the tubule lumen. Example: mammary glands.
9
Q
What is merocrine secretion?
A
Exocytosis of proteins or glycoproteins, Secretory vesicles release their contents by exocytosis. Examples: sweat glands, salivary glands, exocrine pancreas. Called eccrine in sweat glands.
10
Q
What cell types are found in glandular epithelium in merocrine glands (glands that use exocytosis for secretion)?
A
Serous cells
Mucus cells
Myoepithelial cells
11
Q
Serous cells in merocrine glands
A
Stain well with H & E
Secrete proteins
Abundant RER and Golgi in the basal portion of the cell
Secretory granules in the apical cytoplasm
12
Q
Mucous cells in merocrine glands
A
Secrete mucin, made of glycoproteins rich in complex carbohydrates
Mucins stain poorly with H&E – instead stain with periodic acid Schiff (PAS) stain
Abundant RER and Golgi in the basal portion of the cell
Mucin-filled secretory granules in the apical cytoplasm
13
Q
What happens to mucin upon secretion?
A
Upon secretion, mucin becomes mucous, a viscous, jelly-like protective lubricant
14
Q
How are mucuous cells stained?
A
With periodic acid-Schiff (PAS) stain. They do not stain well with H&E
15
Q
How are serous cells stained?
A
H & E
16
Q
Myoepithelial cells in merocrine glands
A
Located between the basal lamina and secretory or duct cells.
They have triangular or elongated nucleus
Have long acto-myosin-rich, contractile processes that surround the epithelial cells
Contraction helps expel secretory product from the gland lumen
Present in sweat, salivary, and mammary glands
17
Q
Where are myoepithelial cells found?
A
Myoepithelial cells are present in sweat, salivary, and mammary glands
18
Q
How are ions and fluid transported across the glandular epithelia?
A
Via ion channels and pumps (ie: Na/K ATPase), using mitochondria as a source of energy. Membrane specializations increase surface area for transport and tight junctions seal off the apical surface from the basolateral surface.. The pumps and transporters are distributed differentially across the surface area.
19
Q
What are unicellular glands?
A
Goblet cells in the lining of the small intestine and in the respiratory epithelium of the trachea
20
Q
What are the similarites and differences between serous and mucous cells in merocrine glands?
A
Both have: ● RER at the base ● Perinuclear Golgi ● Secretory vesicles in the apical portion ● Exocytosis
Major difference is staining: serous cells with H&E, mucus cells with PAS (periodic acid-Schiff)
21
Q
What are sebaceous glands?
A
Multicellular simple, branched, acinar glands. They use holocrine secretion (basal layer of cells proliferate, differentiate into sebocytes,
accumulate lipid droplets, and rupture.
They are associated with hair follicles. The basal layer of cells proliferate and differentiate
22
Q
What is sebum composed of?
A
Sebum is composed of triglycerides, cholesterol, squalene, wax esters.
23
Q
Which glands are responsible for acne?
A
Sebaceous glands.
● Increased sebaceous gland activity at puberty.
● Hair follicle may become plugged.
● Skin bacteria (Propionibacterium acnes) break sebum into free fatty acids.
● Fatty acids cause irritation and inflammation.
● Inflammation attracts neutrophils, further escalating inflammation.
24
Q
What are eccrine sweat glands?
A
Simple, coiled, tubular glands. They use merocrine secretion. They have stratified cuboidal epithelium in the duct and secretory portion.
25
What stimulations sweat secretion?
Cholinergic fibers of the sympathetic nervous system.
26
What are the cell types found in the secretory coil?
Pale (clear) cells
Dark cells
Myoepithelial cells
27
What are pale (clear) cells?
One of the cell types found in the secretory coil. They are pyramidal to columnar in shape. Located at the periphery, resting on the basal lamina. They produce the watery component of sweat and contain abundant mitochondria. They have microvilli and intracellular canaliculli, as well as tight junctions.
28
What are dark cells?
One of the cell types found in the secretory coil. They are pyramidal in shape and located near the lumen. They secrete glycoproteins and proteins, including bactericidal peptides.
29
What are myoepithelial cells?
They are located within the basal lamina and have triangular or elongated nuclei. They contain actomyosin-rich processes, which contract to help expel the secretory product.
30
Describe sweat ducts.
They have a darker staining epithelium than secretory coils. They reabsorb sodium and chloride with abundant Na/K ATPases in the basal membrane. They also have abundant mitochondria and tight junctions.
31
Describe apocrine sweat glands
● Located in the axillary,
areolar and perineal regions
● Simple cuboidal / columnar
epithelium
● Simple coiled glands
● Merocrine secretion
(despite the name)
● The secretory coil is lined by simple cuboidal epithelium and has large lumen
● Associated with hair shafts
● Stimulated by adrenergic
nerve fibers of the sympathetic nervous system, secretory product may contain pheromones
32
What is the composition of sweat and how can it be used as a disease indicator?
Water, Ammonia, Sodium, Chloride, Urea, Uric Acid, Organic Compounds, Bactericidal Peptides, Proteolytic Enzymes.
Altered sweat composition may indicate disease:
● Urea frost in uremia (kidney failure)
● Elevated levels of NaCl in sweat in cystic fibrosis
33
Describe the histological organization of eccrine sweat glands
Stratified cuboidal
epithelium
```
Secretory portion:
● Pale cells:
Function to secrete fluid
Tight junctions
Membrane infoldings
Abundant mitochondria
Intercellular canaliculi
● Dark cells:
Have RER, golgi and secretory granules
secrete proteins
● Myoepithelial cells:
contractile, actin myosin bundles, contract
to expel product
```
Conducting portion:
● Re-absorbs
NaCl and water
34
What is the function and composition of saliva?
To moisten and lubricate the oral cavity, and initiate the digestion of carbohydrates: alpha amylase. Also functions in immune defense: lysozyme, lactoferrin and SIgA. It is also involved in secretion of calcium and phosphate to make acquired pellicle
35
What happens with reduced function of salivary glands?
Reduced function of salivary glands due to disease or radiotherapy can lead to:
speech difficulties, oral mucosa atrophy, and dental carries.
Note, rabies causes INCREASED function of salivary glands.
36
Describe the organization of salivary glands
● Connective tissue capsule
● Septa - extensions of the capsule that divide parenchyma into lobules.
● Connective tissue stroma contains:
- Capillary plexus surrounding secretory
and ductal components
- Nerves that control secretion
--parasymp stimulate, symp inhibit
- Lymphocytes and plasma cells
```
● Parenchyma in the lobules contains salivons:
- Secretory acini or
tubules
- Intercalated ducts
- Intralobular ducts
```
● Interlobular ducts
(in the septa)
37
What are salivons?
A secretory unit found in the parenchyma/lobules of salivary glands, that contain acini, intercalated ducts, and interlobular excretory ducts.
38
What is the drainage pattern of acini?
Acini drain into intercalated ducts, intercalated ducts drain into interlobular ducts, intralobular ducts drain into interlobular ducts located in the septa.
39
Describe salivary gland tumors
```
● 80% are benign.
● Pleomorphic adenoma:
- 65% of benign tumors.
- Accumulation of cartilage-like
material produced by
myoepithelial cells.
```
40
Describe the general organization of salivary glands
● Acini or tubules:
- Serous, mucous, or mixed:
- Serous cells: pyramidal in shape, secrete proteins like sIgA. Also secrete bicarbonate and absorb chloride.
- Mucous cells: cuboidal to columnar in shape, secrete mucin (glycoproteins rich in complex carbs)
- Myoepithelial cell (basket cells): reside within the basal lamina, have long, branched contractile processes that prevent secretory portion dissension and accelerate secretion, they're also present in ducts
● Intercalated ducts:
- Small (4-6 cells in circumference) cuboidal cells that lack secretory granules, they connect the secretory portion to the intralobular duct
● Intralobular ducts:
- More than 6 cells in circumference and lined by simple columnar epithelium. Basal striated in serous glands: basal membrane infolding that house mitochondria. Have active transport of ions (K, bicarb and Na)
● Interlobular ducts:
- Large ducts located in the septa and line with stratified cuboidal-to-columnar epithelium.
41
Compare the amount of ions in saliva and blood plasma
Saliva has 7x potassium, 3x bicarbonate and 1/10 the sodium that the blood plasma has
42
Describe the mechanism of sIgA secretion
Trancytosis:
Exocytosis of sIgA at the apical surface
↑
Proteolysis of the receptor produces sIgA, the IgA in complex with the receptor fragment called secretory component
↑
Endocytosis occurs at base of the acinar cell
↑
IgA binds receptor on an acinar cell and IgA receptor mediates transcytosis of IgA into gland lumen
↑
Serous cells and intralobular duct cells produce IgA receptor
↑
Plasma cells secrete IgA dimer
43
Compare and contrast serous and mucous cells in salivary glands
```
Serous Acinar Cells:
Secrete proteins
(amylase, lysozyme, sIgA)
Mucous Acinar Cells:
Secrete mucus
(heavily glycosilated protein)
```
Common features: Basal RER, Apical Junctional Complexes, Golgi, Myoepithelial Cells, Apical Secretory Vesicles and Small Lumen
44
Describe myoepithelial cells in salivary glands
● Reside within the
basal lamina
● Smooth muscle-like
● Triangular or
elongated nuclei
● Long contractile
processes
● Also present in
intralobular ducts
45
Describe striated interlobular ducts in salivary glands
● Up to 1.5 L of
saliva per day
```
● Saliva
composition:
7x K+
3x HCO3-
1/10 Na+
compared to
blood plasma
```
```
● Basal striations:
Cell membrane
infoldings
that house
mitochondria
```
● Apical surface:
Tight junctions
46
The submandibular gland
Compound tubularacinar gland with both serous and mixed acini, but mostly serous.
Mixed acini: serous demilunes (fixation artifacts)
Serous cells secrete proteins including lysozyme, and some intralobular ducts are striated
47
The parotid gland
Compound acinar gland with ONLY serous acini. Secretes alpha-amylase and other proteins. Intercalated ducts are long, intralobular ducts are striated. Abundance of adipose tissue, look for adipocytes.
48
The sublingual gland
Compound tubuloacinar gland with mostly mucous acini. Some mixed acini with serous demilunes (fixation artifacts). Intralobular ducts are NOT striated.
49
Diagnostic features of the submandibular gland
```
Compound tubuloacinar gland
● Mostly serous acini;
some mixed and mucous
● Mixed acini with
serous demilunes
● Shorter intercalated
ducts
● Mostly striated
intralobular ducts
```
50
Describe the structure of the exocrine pancreas
Compound acinar gland, similar to parotid. It has lobules separated by connective tissue septa. Septa contain blood vessels, lymphatics, nerves and ducts.
51
What are the secretory products of the exocrine pancreas?
```
● Digestive proenzymes:
lipases
nucleases
amylases
proteases
```
● Pancreatic enzymes are inactive proenzymes that get activated by enterokinase cleavage in the duodenum.
● Bicarbonate:
alkaline, neutralizes stomach acid, creating optimum pH for pancreatic enzymes.
52
What is necrotizing pancreatitis?
Pancreatic enzyme-mediated inflammation due to gallstones, alcohol abuse, infections, drugs or trauma
53
Describe the special features of the exocrine pancreas
● Serous acini:
- Polarized serous cells.
- Abundant RER and Golgi.
- Zymogen granules - apical half of cell.
- Secretion is stimulated by cholecystokinin,
a hormone produced by enteroendocrine
cells in duodenum
● Lack of myoepithelial cells.
● Intercalated ducts:
- Protrude into acini as centroacinar cells.
- Produce bicarbonate.
- Lack secretory granules
- Secretin, produced by enteroedocrine
cells in the duodenum stimulates bicarb
● Intralobular ducts:
- Lack striations.
- Also secrete bicarbonate-rich fluid.
● Interlobular ducts:
- Low columnar epithelium.
- Also secrete bicarbonate-rich fluid.
54
Regulation in the exocrine pancreas
1. Acidic chyme stimulates enteroendocrine cells in duodenum.
2. Enteroendocrine cells release cholecystokinin and secretin.
3. Cholecystokinin stimulates proenzyme secretion. Secretin stimulates HCO3- secretion.
55
Major diagnostic feature of the pancreas
Islets of Langerhans, found in the endocrine portion of the pancreas
56
Adenocarcinomas
Malignant tumors of glandular epithelium, some of the most common tumors in adults
57
Acne
chronic inflammation of obstructed sebaceous glands
58
What are the 4 principle layers of the digestive tract?
1. Mucosa
2. Submucosa
3. Muscularis externa
4. Serosa or adventitia
59
What is the function of the mesentery?
Binds the digestive tract to the abdominal wall
60
What are the 3 subdivisions of the mucosa?`
Lining epithelium, lamina propia and muscularis mucosae
61
What are the 3 main functions of the mucosa?
1. protection
2. absorption
3. secretion
It has a lining mucosa and muscularis mucosa
62
At what points does the epithelium of the mucosa change?
The epithelium of the mucosa changes abruptly at junctions or sphincters between the major organs.
63
Describe the lamina proper of the mucosa
The lamina propia is a loose connective tissue resembling the storm of lymphoid organs that contains blood and lymphatic vessels as well as lymphatic tissue and wandering connective tissue cells such as plasma cells and eosinophils. It functions for support.
64
Describe the muscularis mucosae
The muscularis mucosae is a thin layer of smooth muscle that produces movement of the mucosa creating ridges and valleys that facilitate absorption and secretion. It functions in mucosal motility.
65
Describe the submucosa
A layer of connective tissue deep to and supporting the mucosa. It consists of dense irregular connective tissue containing blood vessels, lymphatic vessels and a nerve plexus - submucosal plexus, which controls muscle activity.
66
Where is submucosa found?
In the duodenum and esophagus. Note, it has glands.
67
Where is the submucosal plexus found, what's its function and what is it called?
It's called Meissner's plexus, it is found at the submucosal periphery. Its nerve plexus controls muscle activity.
68
What is the muscularis externa?
The muscular wall of the GI tract, deep to the submucosa. It is composed of two relatively thick layers of smooth muscle: inner circular layer and outer longitudinal layer, between which the myenteric/Auerbach's plexus is located.
69
What is the function of the muscularis externa?
It functions in coordinated contraction for peristalsis: mixing and propelling intestinal contents.
70
What is the serosa/adventita?
The outermost layer of the digestive tract, containing tissue, blood and lymphatic vessels, and nerves. It is serosa when mesothelium (a simple squamous epithelium) is present. It is adventitia when fixed directly to the abdominal or pelvic wall.
71
How do you differentiate between serosa and adventitia?
Serosa is lined with mesothelium - a simple squamous epithelial tissue. Adventitia is attached directly to the surrounding tissue - abdominal or pelvic wall.
72
What are the major features of the oral cavity?
The tongue and papillae
73
Describe the structure of the tongue
The inside of the tongue is made of skeletal muscle arranged in bundles that run in three planes. Between the bundles there are mucosal and serous glands as well as adipose tissue. The dorsal surface of the tongue has an epithelium with elevations called the lingual papillae.
74
What are the 4 types of papillae?
Filiform
Fungiform
Foliate
Circumvallate
75
Which type of papillae have taste buds?
All except filiform! Taste buds are on the dorsal surface of fungiform papillae and the lateral surface of foliate and circumvallate papilla. These three types (fungiform, foliate and circumvallate) have stratified squamous epithelium.
76
Which type of papilla is different from the rest and how?
Filiform papilla are different because they lack take buds and are the only type that have a stratified squamous keratinized epithelium (rather than just stratified squamous)
77
What are taste buds are where are they found?
Onion-shaped sensory structures that contain 50-100 cells. They are found on the dorsal surface of fungiform papilla and the lateral surface of foliate and circumvallate papilla.
78
What are the layers of the esophagus?
Same as the general structure of the GI track: mucosa, submucosa, muscularis external and adventitia (above diaphragm)/serosa (below the diaphragm)
79
What are the function of the digestive system?
1. Derive molecules from food necessary for maintenance, growth, and energy
2. Break down macromolecules into small molecules that are easily absorbed
3. Absorb water, vitamins, and minerals
4. Form a protective barrier between GI tract contents and inside of body
80
What is the esophagus?
- 10 inch (25 cm) long muscular tube consisting of:
- Mucosa
- -Stratified squamous epithelium
- -Esophageal cardiac glands at either end
- Submucosa made of CT, has esophageal glands proper, which create a viscous, slightly acidic mucus that facilities food transport and protects the epithelium
- Muscularis externa:
- -Upper third - skeletal muscle
- -Mid third - both skeletal + smooth muscle
- -Lower third - smooth muscle
81
Where are adventitia and serosa found in the esophagus
Esophagus has adventitia above diaphragm and serosa below the diaphragm
82
Describe the submucosa of the esophagus
The submucosa is made of connective tissue, and the esophageal glands proper. Esophageal glands proper create a viscous, slightly acidic mucus that facilities food transport and protects the epithelium
83
Describe the mucosa of the esophagus
Mucosa consists of stratified squamous (nonkeratinizing) epithelium, lamina proper, muscularis mucosa and esophageal cardiac glands, which secrete a neutral mucus and are found at both ends of the esophagus, but most prominent near the stomach.
84
What glands are found in the esophagus?
Esophageal glands proper, found in the submucosa, create a viscous, slightly acidic mucus that facilities food transport and protects the epithelium.
Esophageal cardiac glands, found in the muscularis external, secrete a neutral mucus and are found at both ends of the esophagus, but most prominent near the stomach.
85
What are the different types of sphincters found in the esophagus?
Upper esophageal sphincter (UES) is made of circular skeletal muscle under voluntary and reflexive control
Lower esophageal sphincter (LES) is a physiological sphincter of thickened circular smooth muscle, not anatomically well defined
86
What are the 6 functions of the stomach?
1. Acts as a mixed exocrine and endocrine organ
2. It continues the digestion of carbohydrates started in the oral cavity
3. Adds an acidic liquid to ingested food
4. Forms chyme with enzyme and muscular activity
5. Pepsin initiates protein digestion
6. Gastric lipase helps digest triglycerides
87
What are the regions of the stomach?
4 at the gross level: cardia, fundus, body, and pylorus, only 3 histologically because the funds and body are identical and thus combined.
88
What are rugae?
Temporary longitudinal folds of the mucosa and submucosa that disappear when the stomach is full.
89
What is the mucosa of the stomach composed of?
A lining epithelium, gastric pits, mucosal glands, lamina propia and muscularis mucosae.
90
What is the lining epithelium of the stomach composed of?
Simple, columnar surface mucosal cells - the secreting sheet
91
What are gastric pits?
PERMANENT invaginations into the lamina proper that serve as ducts for the mucosal glands
92
Describe mucosal glands of the stomach.
Branched, tubular glands that occur in 3 varieties (cardiac, gastric/fundic and pyloric). Each gland has an isthmus, neck and base. 1-4 open into the base of each pit.
93
Describe cardiac glands
Have short pits and short, coiled glands. Most of these glands produce mucus. Some have lysozyme and HCl producing cells.
94
Describe gastic/fundic glands
Have medium pits and long, straight glands. They have 4 major cell types: mucus neck cells, parietal/oxyntic cells, chief cells and enteroendocrine cells.
95
Describe pyloric glands
Have very long pits and short, slightly coiled glands. The glands have mostly mucous cells with a few parietal cells. They also have some enteroendocrine cells that are histologically indistinguishable.
96
Describe the lamina proper of the stomach
Well vascularized and cellular
97
Describe the muscularis mucosa of the stomach
Has 2 layers and sends strands up between glands
98
Describe the muscularis externa of the stomach
It has an extra inner layer of oblique smooth muscle in addition to the usual circular and longitudinal layers
99
Does the stomach have a serosa?
Yes
100
What are Surface Mucous Cells?
Form a secreting sheet on surface and in gastric pits
Secrete an alkaline, viscous mucus with a high bicarcobonate content that protects the stomach’s surface from the acidic gastric fluid. It is an insoluble, cloudy and visible mucous
101
What are mucous neck cells?
One of the 4 cell types found in gastric/fundic glands
Secrete a soluble or mobile mucus
Occur in small groups or singly between parietal cells in the neck of gastric glands
102
What are parietal/oxyntic cells?
- One of the 4 cell types found in gastric/fundic glands
- Secrete HCl and intrinsic factor (a glycoprotein required for vitamin B12 absorption in the ileum)
- Can be binucleate and have intracellular canaliculi for HCl secretion.
- Large eosinophilic cells found in the middle and upper part of the gastric gland
- Acetylcholine, gastrin, and histamine receptors stimulate acid secretion
- Zantac and Tagamet are histamine H2 receptor antagonists that suppress both HCl and intrinsic factor secretion (long term use can cause vitamin B12 deficiency and pernicious anemia)
103
What are chief cells?
- One of the 4 cell types found in gastric/fundic glands
- Typical serous cells
- Synthesize and secrete pepsinogens and lipases
- Found in the basal half of gastric glands
104
What are enteroendocrine cells?
- One of the 4 cell types found in gastric/fundic glands
- Produce gastrin, somatostatin, and ghrelin
- Occur singly or in groups of different varieties at the base of gastric glands
- Their products act on endocrine and paracrine signaling
105
Stomach stem cells
Found in the isthmus and neck of mucosal glands and move upward to replace surface mucous cells that turn over every week. They also move downward to replace glandular cells that turn over more slowly, like 1-2 months
106
How long is the small intestine and what are its 3 segments?
It is 6 meters long:
Duodenum: 25 cm
Jejunum: 2.5 m
Ileum: 3.5 m
107
What are the 3 major functions of the small intestine?
1. Move chyme
2. Absorb nutrients
3. Immunodefense
108
What is responsible for the 400-600 fold increase in the lumenal surface area of the small intestine?
3 structures:
1. Plicae circularis (valves of Kerckring) - permanent transverse circular folds of mucosa & submucosa that increase surface area x 2-3
2. Villi - finger or leaf-like projections of the surface epithelium and lamina propria that increase surface area 10 times
3. Microvilli are projections of the apical plasma membranes that increase surface area 20 times
109
What are the crypts of Lieberkuhn?
Also called, intestinal glands, small tubular glands that extend from the surface epithelium down to the muscularis mucosae
110
What are the 6 major cell types in the epithelium of the small intestine?
1. Absorptive Cell (Enterocyte)
2. Goblet Cell
3. Enteroendocrine Cell
4. Paneth Cell
5. Stem Cell
6. M (microfold) Cell
111
Describe absorptive cells of the small intestine
- Tall columnar cells with a striated border
- Each microvilli is 1 micron tall and 0.1 micron diameter
- Disaccharidases and peptidases are secreted by the absorptive cells and bind to microvilli where they produce monosaccharides and amino acids for absorption
- Lipids are absorbed and reesterified to triglycerides, converted into chylomicrons and released from lateral surfaces into the lamina propr. where they are absorbed by the central lacteals
112
Describe goblet cells of the small intestine
- Unicellular glands that produce acid glycoproteins of the mucin type that lubricate and protect the small intestine
- less abundant in the duodenum and increase in number as you approach the ileum
113
Describe enteroendocrine cells of the small intestine
- Unicellular glands that synthesize hormones and vasoactive peptides
- In the small intestine most occur in the basal portion of the crypts of Lieberkuhm
114
Describe paneth cells of the small intestine
- Exocrine cells found in small groups at base of crypts of Lieberkuhn
- Apical cytoplasm has large, eosinophilic granules that contain lysozyme, phospholipase A2, and hydrophobic peptides called defensins with antibacterial activity
- Crohn’s disease may be a specific disorder of Paneth cells*
115
Describe stem cells of the small intestine
- Located near the base of crypts
| - Move upwards repopulating the crypts and villi in 3 to 6 days
116
Describe M (microfold) cells of the small intestine
- Located in the ileum only.
- Specialized epithelial cells that cover Peyer’s patches.
- Basement membrane beneath M cells is discontinuous.
117
Where is GALT found?
In the lamina propria of the small intestine
118
Describe GALT
- Gut associated lymphoid tissue
- 25% of mucosa in the gut is GALT.
- Peyer’s patches: groups of 20-40 lymphatic nodules found exclusively in the ileum, covered by M cells. Antigens from the lumen are taken up by the M cells and delivered to lymphocytes and other cells in the Peyer's patches
- IgA synthesized by plasma cells.
- SC(secretory component) made by absorptive cells binds IgA dimers forming secretory IgA
119
What are Peyer's patches?
groups of 20-40 lymphatic nodules found exclusively in the ileum, covered by M cells. Antigens from the lumen are taken up by the M cells and delivered to lymphocytes and other cells in the Peyer's patches
120
What is SC (secretory component)?
A 75 kDA glycoprotein synthesized by the absorptive cells and inserted in the basal plasma membrane. Dimers of IgA bind to SC. enter by endocytosis, and exit the apical plasma membrane with SC bound forming secretory IgA, sIgA. sIgA binds antigens, toxins and microorganisms. The sIgA plays a major role in host defense.
121
Describe the region differences in the small intestine
- Duodenum has Brunner’s glands in the submucosa and squat villi. Most of it has an adventitia because it's retroperitoneal
- Jejunum has the most developed plicae circularis, more goblet cells, and longer, more slender villi. Also has a serosa rather than adventitia
- Ileum has the longest villi, most goblet cells, and Peyer’s patches -- unique to the ileum.
122
What are Brunner's glands?
Found in the duodenum of the small intestine, these glands are mostly of the mucous type and secrete an alkaline mucous that helps protect against stomach acid and provide an optimum pH for pancreatic enzyme action.
123
What is the duodenum?
A region of the small intestine. It has brunner's glands, mostly of the mucous type and secrete alkaline mucous t protect against stomach acid. Most of the duodenum has an adventitia, because it is retroperitoneal. The villi are squared off resembling thick cactus leaves.
124
What is the jejunem?
A region of the small intestine with the most highly developed plicae circularis. The villi are longer and more finger-like than in the duodenum and there are more goblet cells. It has a serosa.
125
What is the ileum?
A region of the small intestine. It has the longest villi and the highest number of goblet cells. Peter's Patches are found uniquely here.
126
What are the 5 gross subsections of the large intestine?
1. colon
2. cecum
3. appendix
4. rectum
5. anal canal
127
What are the chief functions of the large intestine?
1. Absorption of water, salts, minerals and vitamins
2. Mucus secretion
3. Storage and elimination of fecal material
128
What are the plicae semilunares?
Temporary fold of the mucosa and submucosa in the colon and cecum
129
Describe the histology of the colon and cecum
- There are no villi, only crypts lined with a simple columnar epithelium with a striated border.
- Goblet cells are especially large and numerous.
- The musculris external is unique. The outer longitudinal smooth muscle is subdivided into three bands called tania coli, with a thin layer of longitudinal smooth muscle between the bands. The bands pucker the colon into haustra.
130
What are tania coli?
Three bands that the outer longitudinal smooth muscle in divided into in the colon and cecum. There is a thin layer of longitudinal smooth muscle between the bands and they pucker the colon into haustra.
131
What is the difference between the transverse and sigmoid colon, versus the ascending and descending colon?
The transverse and sigmoid colon have a serosa. The ascending and descending colon have an adventitia.
132
Describe the vermiform appendix
- The epithelium resembles the colon (simple columnar with a striated border) but the crypts are fewer and shorter.
- The lamina propr. has many lymphoid kicks and lymph nodules that often interrupt the muscularis mucosa.
- The submucosa is often edematous.
- The muscuarlis extra has 2 complete thin layers and no tania.
- There is a serosa.
133
Describe the rectum
- Divided into upper rectum and anal canal
- Upper rectum resembles colon (but no taenia coli and less lymphoid tissue)
- Anal canal is 2.5-4 cm long and has epithelial changes from simple columnar to stratified cuboidal then stratified squamous nonkeratinized (in the ano-cutaneous area) Apocrine glands called circumanal glands can be found in this area
- Crypts and musculris mucosa disappear
- Internal and external anal sphincters
134
Describe the sphincters of the rectum
The inner layer of circular smooth muscle thickens to form the internal anal sphincter - involuntary, and the outer longitudinal layer of the muscularis external is replaced by skeletal muscle that forms the external anal sphincter - voluntary
135
Describe the general structure of the liver
The liver is the 2nd largest organ in the body. it is enclosed in fibrous connective tissue (Glisson's capsule) and divided into 4 lobes: right, left, quadrate and caudate.
136
What are 6 of the liver's main functions?
1. Synthesis of circulating plasma proteins
2. Storage and conversion of several vitamins (ADK) + iron
3. degradation of drugs and toxins
4. involvement in metabolic pathways
5. exocrine function in bile production
6. endocrine-like function
137
What is bile?
Bile is an exocrine secretion of the liver that includes the wastes of erythrocyte destruction and bile salts that act as emulsifying agents to aid gut absorption. It is delivered to the duodenum.
138
What is the liver's endocrine-like function?
The liver modifies the actions of hormones released by other organs including vitamin D and thyroxine conversion and the production of growth hormone releasing factor, GHRF.
139
What is the liver's blood supply?
The liver has a dual blood supply from the hepatic portal vein (75% of liver's blood supply) and the hepatic artery.
140
Describe the blood in the hepatic portal vein
The hepatic portal vein supplies 755 of the liver's blood volume. The blood is rich in nutrients and toxic materials from the intestine, contains blood cell breakdown products from the spleen, and has endocrine secretions of the pancreas and enteroendocrine cells of the GI tract. It's venous blood, depleted of oxygen.
141
Describe the hepatic artery
The hepatic artery carries oxygenated blood that mixes with the venous blood just before it enters the hepatic sinusoids. It supplies ~25% of the liver's blood supply.
142
What is the portal triad?
Portal vein, hepatic artery and the bile duct.
143
Where is the portal triad found?
Portal triad (portal vein, hepatic artery and the bile duct) are found in connective tissue (Glisson's capsule) at the angles of the hexagonal liver lobule.
144
Describe hepatic sinusoids.
Hepatic sinusoids are in intimate contact with the hepatocytes. The sinusoids are radially arranged around the central vein/terminal hepatic venule, which gets larger as it progresses along the lobule and empties into the sublobular veins, which join to form the hepatic veins that empty into the inferior vena cava.
145
How can you distinguish b/w the sublobular vein/hepatic veins and the portal veins?
The sublobular and hepatic veins run alone, versus the portal veins, which are members of the portal triads.
146
What are the 4 structural components of the liver?
1. parenchyma
2. connective tissue stroma
3. sinusoidal capillaries (sinusoids)
4. perisinusoidal spaces (spaces of Disse)
147
Describe the liver parenchyma
One cell thick plates of hepatocytes seperated by sinusoidal capillaries
148
Describe the liver connective tissue strome
continuous w/ Glisson's capsule and branches of the smallest portal canals
149
What is the role of the liver sinusoidal capillaries (sinusoids)?
Sinusoids seperate the plates of hepatocytes
150
Where are the liver perisinusoidal spaces (spaces of Disse) found?
they lie between the sinusoidal epithelium and the hepatocytes
151
Describe the classic liver lobule
The classic liver lobule is a hexagonal cylinder of tissue of 0.7 x 2.0 mm, with the terminal hepatic venule (central vein) at its center.
152
What is the major function of the portal lobule?
The portal lobule emphasizes the exocrine functions of the liver. Since the main exocrine function is bile secretion, the portal lobule has a portal canal at its center, with a triangle formed around it, by connecting lines b/w 3 central veins.
153
What is the structure liver acinus?
The liver acinus is a football shape, with the long axis being a line drawn between 2 central veins and the short axis b/w adjacent portal canals, that lie b/w the central veins.
154
What functions of the liver does the liver acinus give insight into?
1. blood perfusion
2. metabolic activity
3. liver pathology
155
What are the 3 elliptical zones of the liver that surround the short axis?
Zone 1 - contains hepatocytes that are first to receive oxygen, nutrients and toxins from sinusoidal blood. Die last if circulation is impaired and regenerate first.
Zone 2 - intermediate between 1 and 3
Zone 3 - first to show ischemic necrosis and fat accumulation.
156
What are Kupffer cells?
Cells derived from monocytes and members of the mononuclear phagocytic system. They are found in the wall of hepatic sinusoids and extend into the lumen. They function to destroy aged erythrocytes (along w/ the spleen), digest hemoglobin and destroy bacteria. They make up 15% of the liver cell population.
157
What is the perisinusoidal space/space of Disse?
It is the site of exchange of materials b/w blood and liver cells. Hepatocytes have villi that project into this space and increase surface area x 6 times.
158
What are ito cells?
Ito cells are found in in the perisinusoidal space and are the primary storage site for hepatic vitamin A. Under pathological conditions like chronic inflammation or cirrhosis, ito cells lost storage ability and transform into myofibroblasts that make collagen --> liver fibrosis.
159
What are hepatocytes?
Large, polygonal cells with a diameter of 20-20 microns. They make up 80% of the liver cell population and have a lifespan of 5 months but can be replaced after injury, disease or surgery. Their nuclei are large, spherical and centrally located.
160
What are the cytoplasmic components of the hepatocyte?
- -numerous mitochondria
- -elaborate golgi apparatus
- -highly developed RER and SER
- -numerous peroxisomes and lysosomes
- -glycogen (liver depot of glucose that can be mobilized if blood glucose falls)
161
What is neonatal hyperbilirubinemia?
Neonatal hyperbilirubinemia can occur in newborns due to underdeveloped SER in hepatocytes. In this case, bilirubin is not converted to water-soluble bilirubin glucuronide. This is treated by blue light fluorescent light bulbs to transform unconjugated bilirubin.
162
What is the route that bile flows?
Bile flows from the center of the classic liver lobule --> gallbladder --> small intestine.
163
What is the bile canaliculus?
A small canal formed b/w the surfaces of adjacent heptocytes. It has a diameter of 0.5 microns and is isolated by tight junctions. Small microvilli rich in ATPase and other alkaline phosphatases project into the lumen.
164
Where do bile canaliculi empty?
The bile canaliculi empty into intrahepatic ductules (canals of Hering) within the lobule, but close to the portal canal. These ductules are made of cuboidal epithelial cells and they join w/ interlobular bile ducts that are part of the portal triad.
165
How much bile do we make and what's it made of?
The adult liver secretes about 1L of bile per day. It consists of water, phospholipids, cholesterol, bile salts, bile pigemnts and electrolytes.
166
What are bile salts?
Bile salts are emulsifying agents that aid in digestion and absorption of lipids from the gut. About 90% of them are recycled by gut absorption, portal vein transport and hepatocyte re-secretion.
167
What is bilirubin glucuronide?
A bile pigment that comes from hemoglobin breakdown. It Is excreted w/ feces and provides the color.
168
What is the gallbladder?
A hollow, pear shaped organ that can hold about 50 mL of bile. it has a single duct - cystic duct - that receives diluted bile from the liver and discharges concentrated bile to the duodenum via the common bile duct and spinchter of Oddi.
169
Describe the mucosa of the gallbladder.
The mucosa of the gallbladder consists of simple columnar epithelial cells with apical microvilli, complex lateral placations, and concentrations of mitochondria all typical of an organ specialized for absorption of electrolytes and water. It has a lamina propria but no muscularis mucosa.
170
What changes in the gallbladder mucosa when it's full?
The mucosa of the empty gallbladder has rugae or folds that flatten out when it is full. Invaginations of the mucosa form diverticula - Rokitansky-Aschoff sinuses - that can extend into the muscularis. The diverticula increase with age.
171
Describe the muscularis of the gallbladder.
The muscularis has smooth muscle bundles in random orientations. Contractions empty the gallbladder's contents into the cystic duct. The gallbladder has an adventitia where it is attached to the liver and a serosa on its free surface.
